Glucagon is a 29 residue polypeptide hormone, which in cooperation with insulin, mediates homeostatic regulation of the amount of glucose in the blood. Glucagon primarily acts by stimulating certain cells, for example, liver cells, to release glucose when blood glucose levels fall. The action of glucagon is opposite to that of insulin, which stimulates cells to take up and store glucose whenever blood glucose levels rise. Glucagon is produced in the alpha cells of the pancreas, whereas insulin is secreted from the neighboring beta cells.
It is an imbalance of glucagon and insulin that may play an important role in several diseases, such as diabetes mellitus and diabetic ketoacidosis. In particular, studies have shown that higher basal glucagon levels and lack of suppression of postprandial glucagon secretion contribute to diabetic conditions in humans (Muller et al., N Eng J Med 283: 109-115 (1970)).
It is believed that glucagon's effects on elevating blood glucose levels are mediated in part by the activation of certain cellular pathways following the binding of glucagon (GCG) to its receptor (designated GCGR). GCGR is a member of the secretin subfamily (family B) of G-protein-coupled receptors and is predominantly expressed in the liver. The binding of glucagon to its receptor triggers a G-protein signal transduction cascade, activating intracellular cyclic AMP and leading to an increase in glucose output through de novo synthesis (gluconeogenesis) and glycogen breakdown (glycogenolysis) (Wakelam et al., Nature, (1986) 323:68-71; Unson et al., Peptides, (1989), 10:1171-1177; and Pittner and Fain, Biochem. J. (1991), 277:371-378).
The action of glucagon can be suppressed by providing an antagonist, such as a glucagon antibody, such as those described herein. Such antibodies may prove useful in lowering blood glucose levels in diabetes or in other conditions, such as stress hyperglycemia. Furthermore, by lowering glucose levels, it may be possible to prevent or ameliorate certain of the long-term complications associated with elevated glucose levels in diabetic patients.
Anti-glucagon antibodies are mentioned, e.g., in U.S. Pat. Nos. 4,206,199; 4,221,777; 4,423,034; 4,272,433; 4,407,965; 5,712,105; WO2007/124463 and WO2013/081993. Nonetheless, there is a need in the art for novel glucagon antagonists, such as the anti-glucagon antibodies described herein, for lowering blood glucose levels in patients suffering from diabetes and other disorders associated with elevated glucagon levels.